Bulk mixed ion electron conduction in amorphous gallium oxide causes memristive behaviour

Abstract

In thin films of mixed ionic electronic conductors sandwiched by two ion-blocking electrodes, the homogeneous migration of ions and their polarization will modify the electronic carrier distribution across the conductor, thereby enabling homogeneous resistive switching. Here we report non-filamentary memristive switching based on the bulk oxide ion conductivity of amorphous GaO x (xB1.1) thin films. We directly observe reversible enrichment and depletion of oxygen ions at the blocking electrodes responding to the bias polarity by using photoemission and transmission electron microscopies, thus proving that oxygen ion mobility at room temperature causes memristive behaviour. The shape of the hysteresis I-V curves is tunable by the bias history, ranging from narrow counter figure-eight loops to wide hysteresis, triangle loops as found in the mathematically derived memristor model. This dynamical behaviour can be attributed to the coupled ion drift and diffusion motion and the oxygen concentration profile acting as a state function of the memristor.

Conversion of an ultra-wide bandgap amorphous oxide insulator to a semiconductor

“…However, although a large number of AOS materials with bandgaps of~3.0 eV, such as a-In-Ga-Zn-Sn-O, have been developed to date, 2,8,9 semiconducting behavior has never been observed for amorphous Ga 2 O x (a-Ga 2 O x ); only ionic conduction and an insulatormetal transition at a high temperature have been reported. 10,11 A reason for this difficulty is that aliovalent ion doping does not work for amorphous semiconductors except for hydrogenated amorphous silicon; therefore, only metal/oxide ion off-stoichiometry and hydrogen doping would be effective doping methods in AOSs, and consequently carrier control of the conventional AOSs has been conducted mainly by controlling oxygen partial pressure during deposition and thermal annealing (P O2 ) as well as by hydrogen doping. 12 Even these conventional doping methods could not produce semiconducting a-Ga 2 O x .…”

Transmission Electron Microscopy on Memristive Devices: An Overview

“…Additionally, locating the different metal species can also yield information by comparing high and low resistance states. For mixed ionic conductors the conductive properties have been exploited to serve as a memristive material such as in GaOx (Aoki et al, 2014). However, devices relying on cation movement tend to form conducting filaments instead of homogenous switching, as summarized by Valov and Kozicki (2013) in their review article.…”

Evidence for the bias-driven migration of oxygen vacancies in amorphous non-stoichiometric gallium oxide

“…16,17 The crystalline β-Ga 2 O 3 thin film deposited at 700°C is high insulative, and the resistance of the gallium oxide thin films decreases significantly with decreasing the growth temperatures. For depositing at 500°C, the non-stoichiometric and amorphous gallium oxide thin film shows high conductive, and the I-V characteristic curve clearly reveals a pinched hysteretic loop as sweeping the voltage with a cycle.…”

“…For introducing oxygen vacancies in the gallium oxide thin film, tuning the ambient atmosphere and the substrate temperature appear to be crucial factors. [15][16][17] Herein, the nonstoichiometric gallium oxide thin films with an abundant oxygen vacancies were obtained at the low a Authors to whom all correspondence should be addressed. -6 Pa without introducing oxygen, using the pulsed laser deposition technology.…”